In a system which has a master, e.g., a control unit, and a number of slaves, such as consumers, which are connected to the master, information is exchanged between the master and the slaves. Furthermore, the master may also provide power to the slaves. Deliberations are made in this case in order to provide a possibility for transmitting power and information between the master and the slaves.
Electrical interfaces for connecting at least one sensor to a control unit are known, both the power supply and also the data transmission occurring via only two lines. The power is transmitted via a comparatively constant bias current, e.g., via a peripheral sensor interface (PSI5). Alternatively, cyclic power transmission may be carried out, e.g., between or during the transmission of individual bits, for example, in the case of a safe-by-wire operation, which was defined by leading automobile manufacturers and suppliers, or according to an ISO standard. The power transmission may also take place between one or more data words, for example, via a dynamic interface (distributed sensor interface, DSI), or other suitable interfaces, as are offered by Freescale or TRW, inter alia. The cyclic supply has the characteristic that the power is buffered in the sensors for the phases between the power supply. The power transmission takes place frequently in phases having higher voltages and/or according to a fixed time pattern.
Overall, only small power outputs in the range of several watts or currents of at most a few hundred milliamperes have been able to be transmitted using the previous methods.
U.S. Pat. No. 6,459,363 indicates that two wires, via which a control unit and a module are connected to one another, are used to transmit data and power.
A procedure and a system for transmitting power and data via the same line, to which a number of stations are connected, are discussed in U.S. Pat. No. 6,097,761. For this purpose, it is proposed that a bipolar AC voltage be fed into the line, in which a first polarity is only used for the power supply and the data transmission takes place only by amplitude modulation of the pulses of a second polarity. If the pulses of the first polarity are fed in at very low resistance, a large quantity of power may be transmitted to the stations. Only a low power is necessary for the modulation of the data transmission if the pulses of the second polarity are fed in at a high resistance. In this way, only two conductors are necessary, one of which may be replaced by the ground of the system in the simplest case. If three conductors are used, an increased fault safety against the failure of one conductor may be achieved in a very simple way.
A communication system having a master and a number of slaves, which are connected to one another via a bus, is the subject matter of U.S. Patent Publication No. 2007/086,686. In this case, charging times, in which a voltage is applied to the bus, and discharging times, in which the voltage drops again, are alternated according to a fixed predefined pattern. Data are always transmitted when the voltage reaches the value zero during a discharging time.
A similar communication system is discussed in U.S. Patent Publication No. 2007/233920. Time intervals for transmitting power and for transmitting data alternate therein. It is provided that the lengths of the time intervals are fixedly predefined, and a data rate of the transmitted data may be varied.